1. Field of the Invention
The present invention is directed to a longitudinally ribbed plastic film, and to a method and apparatus for producing this film. Such films are used, for example, in pallet wrapping, to prevent moisture and dust damage to the product carried on the pallet. More particularly, this invention is related to such a film which is formed by extrusion through a slot die. The invention is directed particularly to stretch films used for pallet wrapping.
2. Description of the Prior Art
Uniform thickness plastic films exhibit a tendency for puncture and tear propogation when such film is wrapped on a load under high tension. Also, impurities in the resin, such as gel particles, provide points of weakness in the film. To overcome this problem, relatively expensive "clarity" grade resins have been used. Another solution has been the use of tight screen packs and high shear mixing zones to prevent the appearance of gels at the die lip and during melt drawing. However, these steps are unsatisfactory because polymer and/or property degradation result.